The following abbreviations are herewith defined, at least some of which are referred to within the following description of the present disclosure.    3GPP 3rd-Generation Partnership Project    APDU Application Protocol Data Unit    ASIC Application Specific Integrated Circuit    BSS Base Station Subsystem    BBSLAP Base Station Subsystem Location Services Assistance Protocol    BSSMAP Base Station Subsystem Mobile Application Part    BSSMAP-LE BSSMAP-Location Services Extension    BTS Base Transceiver Station    CN Core Network    DSP Digital Signal Processor    EC Extended Coverage    EC-GSM Extended Coverage Global System for Mobile Communications    EDGE Enhanced Data rates for GSM Evolution    EGPRS Enhanced General Packet Radio Service    eNB Evolved Node B    GSM Global System for Mobile Communications    GERAN GSM/EDGE Radio Access Network    GPRS General Packet Radio Service    IE Information Element    IoT Internet of Things    LAC Location Area Code    LTE Long-Term Evolution    MCC Mobile Country Code    MME Mobility Management Entity    MNC Mobile Network Code    MS Mobile Station    MTA Multilateration Timing Advance    MTC Machine Type Communications    NB-IoT Narrow Band Internet of Things    PDN Packet Data Network    PDU Protocol Data Unit    PLMN Public Land Mobile Network    RAN Radio Access Network    RLC Radio Link Control    SGSN Serving GPRS Support Node    SMLC Serving Mobile Location Center    TA Timing Advance    TBF Temporary Block Flow    TLLI Temporary Logical Link Identifier    TS Technical Specification    TSG Technical Specification Group    UE User Equipment    UL Uplink    WCDMA Wideband Code Division Multiple Access    WiMAX Worldwide Interoperability for Microwave Access
At the 3rd-Generation Partnership Project (3GPP) Technical Specification Group (TSG) Radio Access Network (RAN) Meeting #72, a Work Item on “Positioning Enhancements for GERAN” was approved (see RP-161260; Busan, Korea; 13-16 Jun. 2016—the contents of which are hereby incorporated herein by reference), wherein one candidate method for realizing improved accuracy when determining the position of a mobile station (MS) is timing advance (TA) multilateration (see RP-161034; Busan, Korea; 13-16 Jun. 2016—the contents of which are hereby incorporated herein by reference), which relies on establishing the MS position based on TA values in multiple cells.
At the 3GPP TSG-RAN1 Meeting #86, a proposal based on a similar approach was made also to support positioning of Narrow Band Internet of Things (NB-IoT) mobiles (see R1-167426; Gothenburg, Sweden; 22-26 Aug. 2016—the contents of which are hereby incorporated herein by reference).
TA is a measure of the propagation delay between a base transceiver station (BTS) and the MS, and since the speed by which radio waves travel is known, the distance between the BTS and the MS can be derived. Further, if the TA applicable to the MS is measured within multiple BTSs and the positions of these BTSs are known, the position of the MS can be derived using the measured TA values. The measurement of the TA requires that the MS synchronize to each neighbor BTS and transmit a signal time-aligned with the estimated timing of the downlink channel received from each BTS. The BTS measures the time difference between its own time reference for the downlink channel, and the timing of the received signal (transmitted by the MS). This time difference is equal to two times the propagation delay between the BTS and the MS (one propagation delay of the BTS's synchronization signal sent on the downlink channel to the MS, plus one equal propagation delay of the signal transmitted by the MS back to the BTS).
Once the set of TA values are established using a set of one or more BTSs during a given positioning procedure, the position of the MS can be derived through so called multilateration wherein the position of the MS is determined by the intersection of a set of hyperbolic curves associated with each BTS (see FIG. 1). The calculation of the position of the MS is typically carried out by a serving positioning node (i.e., serving Serving Mobile Location Center (SMLC)), which implies that all of the derived TA and associated BTS position information needs to be sent to the positioning node (i.e., the serving SMLC) that initiated the positioning procedure.
Referring to FIG. 1 (PRIOR ART) there is shown a diagram of an exemplary wireless communication network 100 used to help explain a problem associated with the traditional multilateration process in determining a position of a mobile station 102 (MS 102). The exemplary wireless communication network 100 has several nodes which are shown and defined herein as follows:                Foreign BTS 1043: A BTS 1043 (shown as foreign BTS3 1043) associated with a BSS 1063 (shown as non-serving BSS3 1063) that uses a positioning node 1082 (shown as non-serving SMLC2 1082) that is different from a positioning node (shown as serving SMLC1 1081) which is used by the BSS 1061 (shown as serving BSS1 1061) that manages the cell serving the MS 102 when the positioning (multilateration) procedure is initiated. The derived TA information (TA3 1143) and identity of the corresponding cell are relayed by the BSS 1063 (shown as non-serving BSS3 1063), the SGSN 110 (core network), and the BSS 1061 (shown as serving BSS1 1061) to the serving positioning node (shown as serving SMLC1 1081) (i.e., in this case the non-serving BSS3 1063 has no context for the MS 102). The BSS 1063 (shown as non-serving BSS3 1063) can be associated with one or more BTSs 1043 (only one shown) and a BSC 1123 (shown as non-serving BSC3 1123).        Local BTS 1042: A BTS 1042 (shown as local BTS2 1042) associated with a BSS 1062 (shown as non-serving BSS2 1062) that uses the same positioning node 1081 (shown as serving SMLC1 1081) as the BSS 1061 (shown as serving BSS1 1061) that manages the cell serving the MS 102 when the positioning (multilateration) procedure is initiated. The derived TA information (TA2 1142) and identity of the corresponding cell are relayed by the BSS 1062 (shown as non-serving BSS2 1062) and the BSS 1061 (shown as serving BSS1 1061) to the serving positioning node (shown as serving SMLC1 1081) (i.e., in this case the non-serving BSS2 1062 has no context for the MS 102) (i.e., inter-BSS communications allows the non-serving BSS2 1062 to relay the derived TA information (TA2 1142) and the identity of the corresponding cell to the serving BSS1 1061). The BSS 1062 (shown as non-serving BSS2 1062) can be associated with one or more BTSs 1042 (only one shown) and a BSC 1122 (shown as non-serving BSC2 1122).        Serving BTS 1041: A BTS 1041 (shown as serving BTS1 1041) associated with a BSS 1061 (shown as serving BSS1 1061) that manages the cell serving the MS 102 when the positioning (multilateration) procedure is initiated. The derived TA information (TA1 1141) and identity of the corresponding cell are sent directly by the BSS 1061 (shown as serving BSS1 1061) to the serving positioning node 1081 (shown as serving SMLC1 1081) (i.e., in this case the serving BSS1 1061 has a context for the MS 102). The BSS 1061 (shown as serving BSS1 1061) can be associated with one or more BTSs 1041 (only one shown) and a BSC 1121 (shown as serving BSC1 1121).        Serving SMLC 1081: The SMLC 1081 (shown as serving SMLC1 1081) that commands the MS 102 to perform the positioning (multilateration) procedure (i.e., the SMLC 1081 sends a Radio Resource Location services Protocol (RRLP) Multilateration Request to the MS 102).        Serving BSS 1061: The BSS 1061 (shown as serving BSS1 1061) associated with the serving BTS 1041 (shown as serving BTS1 1041) (i.e., the BSS 1061 that has context information for the Temporary Logical Link Identity (TLLI) corresponding to the MS 102 for which the positioning (multilateration) procedure has been triggered).        Non-serving BSS 1062 and 1063: A BSS 1063 (shown as non-serving BSS3 1063) associated with a foreign BTS 1043 (shown as foreign BTS3 1043) and a BSS 1062 (shown as non-serving BSS2 1062) associated with a local BTS 1042 (shown as local BTS2 1042) (i.e., the BSSs 1062 and 1063 do not have context information for the TLLI corresponding to the MS 102 for which the positioning (multilateration) procedure has been triggered).        
Note 1: FIG. 1 is an illustration of an exemplary multilateration process involving three BTSs 1041, 1042, and 1043 associated with three timing advance (TA) values 1141, 1142, 1143 for a particular MS 102. The multilateration can involve more than three BTSs 1041, 1042, and 1043 and more than three TA values 1141, 1142, 1143.
Note 2: FIG. 1 is an illustration of an exemplary wireless communication network 100 showing the basic nodes which are needed to explain the positioning (multilateration) process. It should be appreciated that the exemplary wireless communication network 100 includes additional nodes which are well known in the art.
It is advantageous for the serving SMLC 1081 to estimate the accuracy of the estimated position of the MS 102. The accuracy of the estimated position of the MS 102 depends on the number of cell specific TA estimates 1141, 1142, 1143 (for example) it has been provided with, the accuracy of the individual (cell specific) TA estimates 1141, 1142, 1143 (for example) as well as the MS-BTS geometry, i.e., the true position of the MS 102 relative to the involved BTSs 1041, 1042, 1043 (for example). The accuracy of the TA estimation in turn depends on the accuracy by which the MS 102 is able to synchronize to the wireless communication network 100, and the accuracy by which each BTS 1041, 1042, 1043 (for example) is able to measure the timing of signals received from the MS 102. The accuracy by which the MS 102 is able to synchronize to the wireless communication network 100 is currently specified as a worst-case tolerance. For example, a Global System for Mobile telephony (GSM) MS 102 is required to synchronize with an accuracy of ±0.5 symbol period (a symbol period being 48/13 μs), see 3GPP Technical Specification (TS) 45.010 V13.3.0 (2016-09)—the contents of this disclosure are incorporated herein by reference.
One problem with the existing solution is that the serving SMLC 1081 does not have any information about the TA estimation accuracy of the BTS 1041, 1042, 1043 or about the actual MS synchronization accuracy (MS assessment of the BTS timing). If the serving SMLC 1081 assumes that the accuracy by which the MS 102 is able to synchronize to the wireless communication network 100 is according to the specified worst case tolerance, the estimated accuracy of the estimated position of the MS 102 may be overly pessimistic. Therefore, services requiring a higher positioning accuracy may not be provided with a positioning estimate (i.e., it may be concluded that the target positioning accuracy cannot be realized) even though the actual positioning accuracy may in fact be better than estimated and therefore sufficient. Alternatively, the serving SMLC 1081 may involve more BTSs 1041, 1042, 1043 than are necessary in the positioning process in order to guarantee sufficient accuracy in the estimated position of the MS 102. These problems and other problems are addressed by the present disclosure.